Reconstructing the Subsurface Three-Dimensional Magnetic Structure of A Solar Active Region Using SDO/HMI Observations

TL;DR

This study reconstructs the three-dimensional magnetic structure of a solar active region using high-cadence SDO/HMI data, revealing complex flux-tube topology and providing insights into the subsurface origins of active regions.

Contribution

First-time 3-D reconstruction of a solar active region’s subsurface magnetic structure using high-cadence observations and advanced visualization techniques.

Findings

Active region consists of two major bipoles with tree-like flux-tube structures.

Roots of polarities align along a straight line, top branches are non-coplanar.

Suggests active regions originate from simple flux-tubes undergoing bifurcation.

Abstract

A solar active region (AR) is a three-dimensional magnetic structure formed in the convection zone, whose property is fundamentally important for determining the coronal structure and solar activity when emerged. However, our knowledge on the detailed 3-D structure prior to its emergence is rather poor, largely limited by the low cadence and sensitivity of previous instruments. Here, using the 45-second high-cadence observations from the Helioseismic and Magnetic Imager (\emph{HMI}) onboard the Solar Dynamics Observatory (\emph{SDO}), we are able for the first time to reconstruct a 3-D datacube and infer the detailed subsurface magnetic structure of NOAA AR 11158 and to characterize its magnetic connectivity and topology. This task is accomplished with the aid of the image-stacking method and advanced 3-D visualization. We find that the AR consists of two major bipoles, or four major polarities. Each polarity in 3-D shows interesting tree-like structure, i.e. while the root of the polarity appears as a single tree-trunk-like tube, the top of the polarity has multiple branches consisting of smaller and thinner flux-tubes which connect to the branches of the opposite polarity that is similarly fragmented. The roots of the four polarities align well along a straight line, while the top branches are slightly non-coplanar. Our observations suggest that an active region, even appearing highly complicated on the surface, may originate from a simple straight flux-tube that undergoes both horizontal and vertical bifurcation processes during its rise through the convection zone.